linux-kernel - Re: [PATCH 1/2] sched/fair: pelt: use u32 for util

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Date:   Tue, 5 Jun 2018 09:34:22 +0800
From:   kbuild test robot <lkp@...el.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Morten Rasmussen <morten.rasmussen@....com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Steve Muckle <smuckle@...gle.com>, Todd Kjos <tkjos@...gle.com>
Subject: Re: [PATCH 1/2] sched/fair: pelt: use u32 for util_avg

Hi Patrick,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on tip/sched/core]
[also build test ERROR on v4.17 next-20180604]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Patrick-Bellasi/sched-fair-pelt-use-u32-for-util_avg/20180605-082640
config: i386-randconfig-s0-201822 (attached as .config)
compiler: gcc-6 (Debian 6.4.0-9) 6.4.0 20171026
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

   kernel/sched/fair.o: In function `post_init_entity_util_avg':
>> kernel/sched/fair.c:761: undefined reference to `__udivdi3'

vim +761 kernel/sched/fair.c

   724	
   725	/*
   726	 * With new tasks being created, their initial util_avgs are extrapolated
   727	 * based on the cfs_rq's current util_avg:
   728	 *
   729	 *   util_avg = cfs_rq->util_avg / (cfs_rq->load_avg + 1) * se.load.weight
   730	 *
   731	 * However, in many cases, the above util_avg does not give a desired
   732	 * value. Moreover, the sum of the util_avgs may be divergent, such
   733	 * as when the series is a harmonic series.
   734	 *
   735	 * To solve this problem, we also cap the util_avg of successive tasks to
   736	 * only 1/2 of the left utilization budget:
   737	 *
   738	 *   util_avg_cap = (1024 - cfs_rq->avg.util_avg) / 2^n
   739	 *
   740	 * where n denotes the nth task.
   741	 *
   742	 * For example, a simplest series from the beginning would be like:
   743	 *
   744	 *  task  util_avg: 512, 256, 128,  64,  32,   16,    8, ...
   745	 * cfs_rq util_avg: 512, 768, 896, 960, 992, 1008, 1016, ...
   746	 *
   747	 * Finally, that extrapolated util_avg is clamped to the cap (util_avg_cap)
   748	 * if util_avg > util_avg_cap.
   749	 */
   750	void post_init_entity_util_avg(struct sched_entity *se)
   751	{
   752		struct cfs_rq *cfs_rq = cfs_rq_of(se);
   753		long cap = (long)(SCHED_CAPACITY_SCALE - cfs_rq->avg.util_avg) / 2;
   754	
   755		if (cap > 0) {
   756			struct sched_avg *sa = &se->avg;
   757			u64 util_avg = READ_ONCE(sa->util_avg);
   758	
   759			if (cfs_rq->avg.util_avg != 0) {
   760				util_avg  =  cfs_rq->avg.util_avg * se->load.weight;
 > 761				util_avg /= (cfs_rq->avg.load_avg + 1);
   762				if (util_avg > cap)
   763					util_avg = cap;
   764			} else {
   765				util_avg = cap;
   766			}
   767	
   768			WRITE_ONCE(sa->util_avg, util_avg);
   769		}
   770	
   771		if (entity_is_task(se)) {
   772			struct task_struct *p = task_of(se);
   773			if (p->sched_class != &fair_sched_class) {
   774				/*
   775				 * For !fair tasks do:
   776				 *
   777				update_cfs_rq_load_avg(now, cfs_rq);
   778				attach_entity_load_avg(cfs_rq, se, 0);
   779				switched_from_fair(rq, p);
   780				 *
   781				 * such that the next switched_to_fair() has the
   782				 * expected state.
   783				 */
   784				se->avg.last_update_time = cfs_rq_clock_task(cfs_rq);
   785				return;
   786			}
   787		}
   788	
   789		attach_entity_cfs_rq(se);
   790	}
   791	

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